Precision electric microwelder



Feb. 8, 1966 M. PENBERG 3,234,354

PRECISION ELECTRIC MICROWELDER I Filed Aug. 1, 1962 5 Sheets-Sheet 1 INVENTOR MORTIMER PENBERG ATTORNEY Feb. 8, 1966 M. PENBERG PRECISION ELECTRIC MICROWELDER 5 Sheets-Sheet 2 Filed Aug. 1, 1962 INVENTOR. MORTIMER PENBERG BY 5 E g i i ATRJRNEY Feb.8,1966

M. PENBERG I PRECISION ELECTRIC MICROWELDER Filed Aug. 1, 1962 5 Sheets-Sheet 3 III- l I I I W I l I I JVV I I I I I I I I I I I I L I I6] L.

1 I I I64 I I I I I I I I I l I I I I II8 I I I I I I I I I I I I I I I I I96 I IQB I'AQ I, I I 222 I i 20s 20 2' [@521 I 226 208 am 212 I L 2Ies 2|4 224 2Is 7 2 22o INVENTOR. -I5s I54 232 MORTIMER PENBERG [58 2343? BY 5 Z ATTORNEY Feb. 8, 1966 PENBERG 3,234,354

PRECISION ELECTRIC MICROWELDER Filed Aug. 1, 1962 5 Sheets-Sheet 4.

U U U BRIDGE OUTPUT '%8 I F I T l f l l I /omxss ON c-2 PULSE zoo TRANS- A FORMER f 8 WELD 230 TRANS- FORMER INVENTOR. MORTIMER PENBERG ATTORNEY United States Patent-'6 Ohio Fiied Aug. .1,1%2,Ser. hid-214,051 9 Claims. (Cl. 219- 86) This invention relates to welding, and more particularly to a microwelder for welding tiny components, lead materials and thin film substrates and/or combinations thereof.

Recent developments in space technology have stimulated a need for smaller and lighter'circuit subassemblies in order to, increase the useful pay load of a vehicle. This need for smaller lighter electronic assemblies has been reflected by the development of smaller and more compact electrical components. Sincethe smaller and more compact electrical components and mechanisms have to be connected in an electric circuit, a need has arisen for weldingapparatus which can reliably weld tiny electrical or mechanical components and lead materials to other electrical or mechanical element's.

More particularly, it would be desirable to provide a welding apparatus which "can weld tiny pieces of metal to tiny pieces of insulating material such as glass. In such application as when the metal and "insulatorare to .be part of anelectrical component, such as a, transistor or thin film circuit, it is not possible to place the work between opposed electrodes, as with conventional weld ingmachines, because one of the surfaces is an insulator. Thermal compression bonding machines "are not satisfactory because'the heated region of the work is not localized in the weldvarearand heating the'entire component during the welding cycle coulddestroy it. What is needed, therefore, and comprises a principal object of this invention is to provide an electrical welding machine which can reliably weld tiny components and lead materials together.

A further object of this inventionis to provide'a reliable electrical microwelder wherein electrodes-are applied to only one side of the workin such a way that the-heated region of the work is precisely localized.

' The microwelder in. its broadest aspect comprises an electrical power supply capable of delivering pulses of electrical energy to a probe-like electrode structure. The electrode structure is formed from separate electrode elementssecured togetherland separated by'an insulator to form aunitary rigid structure or probe. Thiselectrode structure is connected to the electrical power supply in such away that during a'weldin-g cycle, current flows down one of the electrode elements through a localized region of the work, then up the other electrode element to complete the circuit. Theelectrode structure is associated with an appropriate mechanism for moving it in contactwith the work. The electrical circuit. for the microwelder includes an indicator circuit to indicate when the electrical contact between the electrodes and :the work is correct.

These-and other objects of this invention will-become more apparentwhen read in the light of the accompanying drawings and specification, wherein:

FIGURE 1 is a perspective view of the microwelder;

FIGURE 2 is a longitudinal sectional view of one embodiment of the electrode structure for. the microwelder;

FIGURE 3 is a transverse sectional view taken on the line 3-3 ofFIGURE 2;

FIGURE 4 is an enlarged longitudinal sectional View of the lower portion of the electrode structure shown in FIGURE 2;

FIGURE 5. is a transverse. sectional view of a modified concentric electrode structure;

3,234,354 Patented Feb. 8, 1966 "ice FIGURE 6 is a longitudinal sectional jview, of another modification of the electrode structure;

FIGURE .7is a circuit diagram showing the power supply for the microwel'der;

FIGURE 8fis a series of diagrams showing the wave forms at variousparts of the electrical power supply;

FIGURE 9. is. a partially diagrammatic and partially schematic view of amodified (power supply control circuit showing a feedback relationship between the electrode structure and the welding pulses delivered by the p w rp y;

FIGURE 10 is a-partly-di'agrammatic and partly sche-. matic View showing another modified control ,circuit .designed to overcome a poor electrical contact between the electrode structure and the, work by increasing the pressure" of the electrode structure upon the Workfsinfacei FIGURE 11 is an elevational view-of a portion of the electrode structure used with the modification shown in FIGURE 10 and showing a solenoid holding mechanism associated with'the electrode structure;

FIGURE 12 is a transverse sectional view-takenonthe line'1212'of FIGURE 11; and

FIGURE 13 :is a transverse sectional view similar to that shown in FIGURE 12, but with the solenoid holding mechanism de-energized.

Referring nowtoFIGUREI of the drawings,-the microwelder, indicated generally by the reference numeral 10 comprises a support housing 12 with a horizontally extending base memberl l; B-ase me-mber -14 is provided with an upstanding portion 1 6 on-which" a Work supporting member 18 is mounted. The position of the work supportingmember-wcn the upstanding portion 16is controlled by an actuating lever 20'in'a manner well-known in the art. A microscope 22 is mounted on the b'asemember 14 for viewing the micro-elements tohe'welded. In additioma fixed arm 24 extends horizontally out from the upper end of the support housinglz'over the work supporting member .18 for holding a pair of adjustably mounted lights 26 whereby the work can be properly illuminated.

An electric motor 28 ismounted inside the support housing 12. The drive sh-aft29 of the motor is connected to at-hreaded shaft 30 by means of a tcothedbelt 32. The threaded shaft Sitis in threaded engagementwith a fixed tubular nut B l-whereby rotation ofv the threaded shaft 30 in one-direction causes theth-readed shaft30sto move upward with .respect to the tubular nut 34, and rotation of the threaded shaft 30rin the opposite direction causes the .threaded shaft 30 to movedownwardrwith respect to the tubular nut 34.

An arm 36 is secu-red;to. and movable with threaded shaft 30. The arm; 3:6;extends through a-vertical slot 38 in the front wall of the housing 12. The free, end 40 of the arm -36-is providedawith a vertical bore 41 for receiving and holding an electrode structure 42. With this arrangement, operation; of 'the ,motor 28 in one. direction causes theelectrode structuredz to move toward the work supporting member 18;.and operation of the motor 28 gin the opposite direction causes the, eleetrodestructure 42 to move away-fromrtheyworkt'supporting member 18*. Although the: example. shown "in the drawing and described above utilizes an elect-ricrnotor 28* for control of the-electrode structure 42, it 'is apparent that the electrode structure: 42c-ould be controlled byother mechanisms such as a hydraulic'or pneumatic motor.-

The electrode structure 42' has apencil-likc appearance (see FIGURE 2). As shown in FIGURE 3, the electrode structure 42comprises electrode-elements 44 and 46 which are separated from each other by an insulating material 48 and covered by an insulator 50. The electrodes 44 and 46 are semi-circular in cross-section and are bonded to the insulating material 48, so with each other to form a rigid structure.

FIGURE 4 discloses the electrode structure 42 in contact with the work 55, the lower ends or tips 43 of the electrodes 44 and 46 being in engagement with a surface of a conductive member 52 of the work 55 which is to be microwelded to a conductive or nonconductive mem: ber 54 of the work 55. The dotted lines passing through the work 55 indicate the path of the current between electrodes 44 and 46. It is noted that the lower ends 43 of the electrodes 44 and 46 as seen in FIGURE 2 appear to be pointed. However, this view is misleading because of the size of the micro-elements to be welded (.005" to .01). In practice, the lower ends 43 of the electrodes 44 and-46 would have to be flattened as shown in FIG- DRE .4. p By bonding the electrodes 44 and 46 together, separated only by the insulating material 43, the spacing between the electrodes 44 and 46 is absolutely fixed. This feature is extremely important in microwelding because minute variations in the spacing of the electrodes would have a substantial eifect on the heating applied to the work and consequently to the integrity of'the weld. With this arrangement, the problem of quality control in microavelding operations is vastly simplified. In contrast, where the electrodes are in spaced relation to each other with an open space therebetween, the problem of quality control in microwelding is extremely diflicult. This is because very tiny variations in the spacing of the electrodes, such as might be produced by room vibration or thermal expansion of the mounting structure of the electrodes, could have substantial effects on the quantity of heat delivered to the work. I The electrode structure 42 as to cooperate shown in FIGURES 2 and 3 of the drawings utilizes electrodes 44 and 46 which are generally semicylindrical in shape. It is apparent, however, that the electrode structure could have other possible configurations. For example, the electrode structure 56 shown in FIGURE of the drawings is formed from an outer tubular electrode 58 and an inner cylindrical electrode 60 separated from each other by a tubular dielectric 62.

With the electrode structure shown in FIGURE 3 or 5, when the work ocntacting or lower ends 43 of the electrodes of the electrode structure 42 or 56 become worn, they can be reshaped without disturbing the spatial relationship between the electrodes.

The electrode structure 42 is provided with afixed collar 63 secured thereon by any suitable means. A flanged sleeve or bushing 65 'is mounted on the 'free end 40 of the arm 36 which holds the electrode structure 42 with the flanged upper end 67 of the sleeve 65 adapted to 4 of the electrode structure 42, as influenced by the number of pellets or weights 66 placed in or on the cup-shaped member 64. This arrangement substantially eliminates variations in the force of contact between the electrode structure 42 and the work 55. It also reduces unpredictable variations in the pressure applied to the work area under the tips 43 of the electrodes 44 and 46 and in the current flow through the work 55; consequently, unpredictable variations in the heat supplied to the work area are reduced. This arm-electrode arrangement provides in FIGURE 6 wherein the individual electrodes 7%) and 72 are generally wheel-shaped and are secured together with an insulating material 74 between them to form a; generally rigid unitary electrode wheel 76. The electrode a wheel 76 is rotatably mounted in the tines 78 of a fork like support member 80.

. an internally mounted travel stop ring or washer 86 through which a reduced upper portion 68 of the forklike support member 80 extends. This reduced upper. portion 88 bears against a spring loaded pressure plate 90. 1

One end of a coil spring 92 bears against the spring loaded pressure plate 96 and the opposite end bears against a cup-shaped spring retainer 94 movably mounted inside sleeve bearing 82. A second coil spring 96 is also mounted inside the sleeve bearing 82 with the opposite ends of the coil spring 96 hearing against cup-shaped members 98 and 106.

A threaded tube 162 is mounted in the upper end of sleeve bearing 82 and a calibrating screw 164 is threadedly mounted therein. The lower end of the calibrating screw 164 is adapted to engage the cup-shaped member 164) engaging the upper end of the second coil spring 96] A microswitch 166 is secured to the outer surface of the shell member 84 surrounding the sleeve bearing 82. The microswitch 166 is provided with an actuating arm llil which extends through the sleeve bearing 52 between the cup-shaped n1embers98 and 94. i 3

. With this arrangement, the calibrating screw" 164 is rotated until spring 96 is compressed a predetermined amount. Only when an opposing pressure on the electrode wheel 76 exceedsthis amount will the force transmitted by the electrode wheel 76 to the coil spring 92 bear against collar 63. The external diameter of the inter- V mediate portion of sleeve 65 snugly fits in a bore 71 pro vided in the arm 36 with the free end 40 of arm 36 being embraced by the upper and lower flanges 67 and 69 of the sleeve 65.

A cup-shaped member 64 is attached to the upper end of the electrode structure 42 remote from the work contacting portions or tips 43 of the electrodes 44 and 46' (see FIGURE 2). This cup-shaped member 64 is adapted to be filled with pellets 66 or to carry a weight-loaded adapter or a spring-loaded carrier. With this arrangement, as the electrode structure 42 is moved toward the work by motor 28,-collar 63 rests on and is supported by the upper'flange 67 of sleeve or bushing 65. However, when the work contacting portions or tips 43 of the electrodes 44'and 46 of the electrode structure 42 contact the work 55, continued downward movement of arm 36 causes the sleeve 65 to move downwardly with respect to the electrode structure 42 to ardotted line position shown in FIGURE 2, while at the same time, the sleeve 65 holds the electrode structure 42 in an erect position. As a consequence, the force of contact between the work contacting end portions or tips 43 of the electrodes 44 and 46 and the work 55 will depend only on the weight exert enough pressure on the actuating arm to cause it to move upwardly and thereby close the microswitch 166. The microswitch 106 is connected in the power supply circuit of the microwelder in such a manner that the pressure of contact of the electrode wheel 76 with the work must exceed the compression imposed on spring 96 by the calibrating screw 164, in order to displace the actuating arm 110 of the microswitch 106 for closing a relay circuit to permit the electrode microwelder to operate. In this way, the force of contact between electrode wheel 76 and the work can be accurately controlled so that the current flowing through the work between the electrodes 70 and 72 of the electrode wheel 76 will not be adversely afiected by a poor contact caused by inadequate electrode structure pressure. It is also apparent that a hydraulic or pneumatic system could be used instead of a spring arrangement to perform the same function.

An electronic power supply circuit indicated generally by the reference numeral 112is provided for the microcausing it to" become conductive.

abruptly becomes noncon'ductive. the m'onosta-ble rnulti'vibrator 114-to revertto'its initial condition wherein transistor 1219 becomes conductive again while transistor 122 becomes non'conductive.

"transistors 120 and 122 along with a unijunction transistor 124. capacitor 126, a variable resistor 128, and a resistor 130 is associated with the unijunction transistor 124 for controlling thepulsefperiod of the multivibrator 114. Tran- "sistor 120 is'biased so his normally on, or conductive,

In addition, a timing circuit comprising a while transistor122is biased so it is normally oft, or nonconductive. When a voltagepulse from any source is appliedto input .terminal'129, the rise inpotential of the base of'transistor 120- causes it to-become nonconductive.

This decreases the'potential ofthebase of transistor 122. This occurrence causes the voltage onwire 132 whichrisconnec'ted tothe collector of transistor 1 22 to abruptly increase. While'this is happening,'the timing circuit-comprising capacitor 126 'and resistors128 and 130 causesthepotential of the base of unijunction tran'sistor124 toagraduallydrop until it This occurrence causes The above described circuitis generally conventional in design and is describedon page 145, FIGURE 13.17 in the bookgGe'neral Electric Transistor Manual, 5th edition, published'by the'General :ElectrieCompany. 'The operation of the monostable multivibrator 114 causes a square wave'to appeanon lead wire 1 32. The duration or 'periodof the sq'uarewave may 'be controlled by the adjustment of variable resistor 1 28, whilethe amplitude of the "squarewave'rnay be controlledby adjustment of variableresistor 1'34inleadwire 1'32. -Lead wire 132 'is connected to the input lead 136 in the electronicswitch circuit 118through a rectifier 13s.

The one-shot 'rnon'ostable -multivibrator 116 is identical-in' design and operation to multivibrator 114 and square wavetpulse-whose amplitude is substantially less than-the amplitude of the square wave pulse put out by r'nonostable multivibrator 114.

As shown inFlGURE 7 of the drawings,-input lead 1361s connected to thebase' ofiriput transistorplfill in switch circuit '118. The collectorof transistor 151i is connected to the base of-amplifier transistor 152. Both transistors'150and 152 are'biased so theyare conductive *whn any square wave pulse from multivibrators 114 or -116'appears on input lead wire-136.

The phase con-trolled switch circuit 118 is powered 'by a standard: 115' volt A.-C. source connected to input "power leads-and 156: inwhich-a conventional control sWitch'158"isrnounted. An indicator lainpdfitl is placed across'thep'owerleads 154- aridr156 to indicate thatythe power is on when'it'is lighted.

The Ax-C. phase-controlled switch circuit 118 includes *diodesy162,"164, 166, and 16$ which are connected togethep in 'a bridge circuit to form -a-full-waverectifier. The output of the rectifier'appearsat terminal-17tl. Ter- 'm'inal 170 is connected to oneend of-a Zener diode 172 through a voltage dropping resistor-174. -Withthis arrangement, the sinusoidal inputvoltage 1%, indicated "by wave form ain FIGURE 8 isbothrectifiedandmodified by the co-action between the silicon-controlled rectifiers to be described below, and which *functionas a short for the bridge circuit, and the full-wave bridge rectifier. Consequently, the actual bridge output voltage 178 ap- -pear'ing' at terminal 170 has a wave form 8b, shown in fies the bridge outpurvoltage '8b sothat the voltage 182 appearing on terminal 180' has a wave form8c of FIG- URE 8. i

This clipped voltage 182 'appearingon the common lead wire 184 in cooperationwith the-amplitude of the square-wave pulse delivered by-one of the multivibrators 114 or 116, charges a c'apacitor'186 whiletransistor 152 is conducting. The time constant-for charging capacitor 186 is dependent on the magnitude of itsca-paci-tance, the magnitude of resistor-188,-andthe magnitude of the amplitude of the square wave output from-one of themultivibrators 114, 116.

Terminal 190,-connected to oneiside ofcapacitor 186, is connected toem-itter-192- ofunijunction transistor-19 4. The voltage 195 across capacitor 186 -hasa wave form as shown in"8d of FIGURE 8. When-thisvoltage rises to the correct predetermined level, transistor l94 becomes conductive, thereby permit-ting capacitor-186 to discharge .through the primary coil196 of apulse transformer 198;

this condition=causes anabrupt drop in the potential across capacitor 186. The voltagepulse-200 caused by the discharge (if-capacitor 1S6'through the unijunction transistor-194 and through primary coil196 of the pulse transformcr'198 is shown as-wave'forrn S'ein FIGURE 8.

Pulse transformer 198 is. providedwith two secondary coilsQllZ and 294. The opposite terminals or the secondary coil 202' are connected tothe-gate terminal or cathodemdof the silicon controlledrectifier206 and to circuit lead 211 Similarly the opposite terminals of the secondary coil 204 are connectedto the gate terminal of cathode 2120f siliconcontrolled rectifierll land to lead 216. Power lead'154is connected'to' one side of leads 210 and 216through the primary coil 218 'of'the" welding transformer 220 and power lead'156 is connected to .the

opposite side 'of leads 210 and216.

If'neither ofthe sil-iconcontrolledrectifiers 206 or 214 are turned on, welding power'frorn' the sinusoidal 115V power supply cannot'flow through the primary coil 218 of the 'weldtransformer'ZZtlbecause bothof the silicon controlled rectifiers 206,114 act'as open'circuits.

However, if the polarity between the cathode, and anode of either of the silicon controlled rectifiers 20:6, 214 has aproper'relationship' at a time when a'pulse is applied to the gate of the cathode of the silicon controlled rectiiier, then it becomes and remains conductive until the Voltage between the cathode and anode'ofthe silicon controlled rectifier becomes zero inthe course ofits alternation. 'In' particular, if the voltage from lead 154 is momentarily positive on lead wire 222,, the potential of anode224 of silicon controlled rectifier 214will'be positive with respect to the cathode 212. Hence, if "a pulse 200 isapplied to'the gate of" silicon controlled pulse 200 from the pulse transformer'1'98 would be ineffective in turning silicon controlledrectifier 206"on and'silicon controlledrectifier 2tl6- would still appear as an open circuit in lead 210.

When the potentialon-lead wire 222 alternates and becomes negative instead of "positive, silicon controlled rectifier 214 turns olr" as the potential between itscathode -212 and' anode 224 becomes zero and the potential of anode 224 of silicon contro1led'rectifier214 will become negative "with respect'to 'the cathode 212. As a result, agate pulse 200from pulse transformer 198 would be inetfective in turning the silicon controlled rectifier 214 on under these conditions. However, when the potential onlead 222 becomes negative, the potential on lead 228 becomes positive.

aasasea Hence, the anode 226 'of silicon controlled rectifier 206 becomes positive with respect to the cathode 208. As a result, when gate pulse 208 from pulse transformer 198 is applied to silicon controlled rectifier 206 under these conditions, it becomes conductive and a circuit is completed between leads 222 and 228 through lead 210. Consequently, a power pulse can flow through the weld transformers primary coil 218 of weld transformer 220.

In summary to this point, it is clear that no power pulse can flow through primary coil 218 of weld transformer 220 unless one of the silicon controlled rectifiers 206 or 214 is conductive. It is apparent, therefore, that by controlling the time from the beginning of the A.-C. cycle, when a gate pulse appears at primary coil 1% of pulse transformer 198, the shape of the power pulse passing through the weld transformer coil 218 can be controlled.

Referring now to wave form 8 in FIGURE 8, the dotted portion of sinusoidal wave form 230 indicates portions of a sinusoidal pulse supplied by the power input leads 154 and 156 when the silicon controlled rectifiers 206 and 214 are nonconductive. However, by referring to the wave form Se in FIGURE 8, it is apparent that as soon as a tiny pulse 280 appears at primary coil 196 of pulse transformer 198, one of the silicon controlled rectifiers 266 or 214 becomes conductive, permitting the remaining portion of the voltage cycle to pass through primary coil 218 of the weld transformer 220.

As stated above, the silicon controlled rectifiers 266 and 214 turn off each time the voltage between their cathodes and anodes passes through zero. Hence, the energy in each voltage pulse 230 delivered to the primary coil 218 of the weld transformer 230 can be adjusted as desired by varying the size of capacitor 186, or the size of resistor 188, or the amplitude of the square wave pulse from the multivibrator 114 which together determine the period of time it takes to cause unijunction transistor 194 to break down and deliver a voltage pulse 280 to primary coil 1% of pulse transformer 198.

=Multivibrator 114 is set so the period of its squarewave voltage pulse is large in comparison to the period of a 115-volt A.-C. power supply provided to input leads 154 and 156. As a consequence, the A.-C. switch circuit 118 will remain in operation only so long as a positive pulse appears on input lead 136. During this time, a train of voltage pulses each containing a precise and controlled quantity of energy will pass through pri mary coil 218 of weld transformer 220 each time multi vibrator 114 provides a square wave pulse. By controlling the period of the square wave pulse, it is apparent that the number of pulses passing through the weld transformer 220 can be accurately controlled.

If switch 140 is closed, then after the multivibrator 114 completes its square wave pulse, the reversion of multivibrator 114 to its stable condition triggers a second square wave pulse in multivibrator 116. The amplitude of this square wave pulse described above is smaller than the amplitude of a square wave pulse from multicaused by abrupt cooling.

In resistance welding techniques, the heat generated in the work depends on the magnitude of the current flowing therethrough. This in turn depends on the resistance between the electrodes contacting the work. If the resistance between theelectrodes and the work varies, the current fiow and the heat applied to the work will likewise vary; Since the resistance between the electrodes and the work can vary because of insuflicient pressure, or because of the presence of foreign matter, the energy in the welding pulses actually flowing through the work can become unpredictable, thereby affecting the quality control of the microwelds. To prevent this from happening, it is desirable to provide means for indicating when the contact between the electrodes and the work is proper, or when for some reason, the contact between the electrodes and the work is so poor that substantial and undesired resistances are introduced in the circuit.

As shown in FIGURE 7, the opposite terminals of the secondary coil 232 of the weld transformer 220 are each connected to one of the electrodes 44 and 46. Even if no welding pulse is passing through the primary coil 218 of the weld transformer 220, a small current will pass therethrough due to the action of the bridge rectifier defined by diodes 162, 164, 166, and 168 supplying a small quantity of current to the Zener diode 172. If a suitable voltmeter 234- is connected between these electrodes 44 and 46 as shown, then an increase in the potential between the electrodes 44 and 46 caused by an improper contact with the work 55 could be detected. Hence, the voltmeter 234 provides an indication of whether the electrodes 44 and 46 are in proper contact with the work 55.

The extent to which the reading on voltmeter 234 departs from the voltage between electrodes 44 and 46 which corresponds to a good contact with the work 55, can provide a means for controlling the IPOWGI' supply so that the amplitude and number of the power pulses delivered to primary coil 218 of weld transformer 220 will increase automatically to compensate for the poor contact between the electrodes 44 and 46 and the work 55. This requires a feedback circuit arrangement such as disclosed in FIGURE 9.

In the modified power supply circuit indicated generally by the reference numeral 235 shown in FIGURE 9, leads 236 and 238 connected to the terminals of the secondary coil 232 of the 'weld transformer 220 are connected between electrodes 44 and 46 to the opposite side of a diode-type bridge rectifier indicated generally by reference numeral 240. The negative pulsating voltage output from the bridge rectifier 240 appears on terminal 242. This pulsating voltage output is smoothed by a sufficiently large capacitor 244 and is fed into one side of a differential amplifier 246. The opposite side of the differential amplifier 246 is connected to the slide contact of a grounded variable resistor 248. A supply voltage is connected to the side of the variable resistor 248 opposite the grounded end. The output voltage of the diiferential amplifier 246 appearing on terminal 250 represents a voltage which is proportional to the difference 7 between the correct voltage between electrodes 44 and 46 which would occur when these electrodes are making a good contact with the work 55, and the actual voltage which does occur. Terminal 250 is connected to the switch circuit 118 at input terminal 252 (see FIGURE 7).

By this arrangement, the negative differential voltage applied to the input terminal 252 increases the time constant for charging capacitor 186, thereby decreasing the energy supplied by the weld transformer 228. Consequently, the decreased energy in the power pulses passing through the primary coil 2 18 during a welding operation compensates the electrode structure 42 automatically for the increased resistance between the electrodes 44 and 46 and the work 55. In this way, the quality control and the reliability of the welds formed by the microwelding apparatus is maintained.

Another method of compensating for a poor contact between the electrode structure 42 and the work 55 is by increasing the pressure which the electrode structure 42 exerts against the work 55. The modified control circuit indicated generally by the reference numeral 254 and shown in FIGURE 10 of the drawings, accomplishes this by connecting leads 236 and 238 leading from eleci 264 to close.

9 trodes 44 and 46 to-an amplifier 256. 'Lead- 236 from electrode 44- passes through normally closed contacts 258 ofa rel-ay260. The terminals of the coil of relay 260 are connected across leads 236 and 238 respectively.

The 'relay coil 260 is designed so that when a power pulse passes thro'ughprim'ar'y coil 21% of weld transformer 220, the voltage-across leads 236 and238 will be sufii'cient to cause therelay 260 to'open the contacts 258 so that the motor '28 will: not operate.

The output *of amplifier 256 is connected across the ter- "minals of the coil of a relay 262. The relay 262 is associated with a pair of normally open contacts 264 and when the input voltage to amplifier 256 is" sufficiently large, the power delivered to relay 262 causes cont-acts Power lead 266 connected to power input I lead 154 is connected to one' side of the normally open contacts'264. The opposite-side of the contacts 264 is connected to one side of a holding solenoid coil'268 and to motor 28. The opposite ends of the holding solenoid 268 and the motor 28 are connected through a lead 270" delivered to theprimary coil 218. This voltage is'sufiicient when amplified by amplifierZSG to cause relay 262 to close contacts 264. Thiscauses motor '28 to begin operation and move the electrodes '44 and 46 into contact with the work 55. As the electrodes 44 and 46' contact ithework 55, the resistance between the electrodes 44 and46 and the work'55 will decrease as the force of contact increases until the electrodes 44 and 46 make a good contact with the Work 55, whereby the voltage between electrodes 44 and 46 drops to a minimum. This causes relay262 to open contacts. 264, thereby cutting ofi power to motor 28 and releasing electrodes 44 and'46 held by the holdingsolenoid '268.

'In this particular embodiment, the holding solenoid 268 is mounted on the arm'36 seen in FIGURE 11' of the drawings. -Arm3 6 is, in this-particular embodiment, provided with an integrally formed semi-circular clamp member 272 (see FIGURES 12 and 13). An opposed semi-circular clamp member 274 is associated with semicircular clamp member 272 -and is attached thereto and separated therefrom by compressed coil springs 276. Both of the semicircular clamp memhers-272 and 274 are formed from a magnetic material, and when the holdingv solenoid 268 is actuated, the clamp members 272 and 274 are magnetized and drawn together, as shown in FIGURE 12. This causes the clamp members 272 and 274 to tightly embrace the-electrode structure 42 so that as the arm 36 moves vertically with respect to the work 55, the electrode structure 42 is carried with it.

When power to the holding solenoid 268 is cut off, the compression .in springs 276 forces the semi-circular clamp members 272, 274 to separate sufficiently so that the electrode structure 42 is freely movable therein. With this arrangement, until electrode structure 42 makes a good contact with the work 55, motor 28 remains on, continually increasing the force of engagement between the electrode structure'42 and the'work 55. However, after a 'good electrical contact with thework 55 is obtained, solenoid 268 is d-eenergized'and the sole pressure exerted by the electrode structure 4 2 against the work SS'is caused by the weightof' the electrode structure'42 alone. Consequently, the initial pressure between the electrode structure42 and the work 55 is the same for As aresult, the problem of each Welding operation.

quality control in microwelding is simplified.

' It is to be understood that the forms of the invention herewith shown and described are to be taken as preferred examples of the same, and that various changes in the shape, size and arrangement of the parts maybe 1'0 resorted "to without departing from the spirit of this inventionorthe scope of the claims.

I claim:

1.- A mi'crowelder of the class described comprising a support, arod-like electrode structure, a motor associated with said support and said electrode structure whereby operation'of said motor causes saidelec'trode structure to engage or disengage the work; said electrode structure "beingat least bilaterally symmetrical and comprising at least two electrodes separated by arelatively thin layer of insulating material and'bonded'together in a fixed spaced relationship to form a unitary structure, the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operativeend portion for the'electrodestructure having theappearance of thewrit'ing'tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil; said electrode structurebeingsufficiently rigid 'so that the work contacting portions of the electrodes can be formed small enough to-precisely localize the energy applied to the work without causing appreciable deformation due to the force of engagement between the electrode structure and the work, an electric power supply, the electrodes forming said electrode structure being connected to said power supply in such a way that during delivery of weldingpower while theelectrode structure is engaging one electrically conductive side of the work, current flows from the 'power supply down one electrode through the workand back up the-other electrode to complete the circuit, and means for precisely regulatingthe force of engagement betweenthe electrode structure and the work to regulate and standardize the electrical resistance'between the electrode structure and the work.

"2.A mi'cr'owelder of the class described comprising a support, a rod-like electrode structure, motor means mounted on said support, a shaft connected to said motor means insucha Way that operation of said motor 'means causes saidshaft to rotate, an arm slidably mounted on said shaft andconnected thereto in such a way that rotation of saidshaft causes said armto move axially with respect to said shaft, said electrode structure being mounted on'said arm whereby operation of said motor means in one direction causes said shaft to rotate so that the arm and the electrode structure carried by the arm moveinto engagement with the work, while operation of the motor means in the opposite direction causes said arm and said electrode structure to move away from the work; said electrode structure being at least bilaterally symmetrical and comprising at-lea-st' two electrodes sepa rated by a relatively thin layer of insulating material and bonded together in a fixed spaced relationship to form a unitary structure, the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operative end portion for the electrode structure having the appearance of thewriting tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil; said electrode structure being sufliciently rigidso thatthe work contacting portions of the electrodes can'be formed small enough to precisely localize the energy applied to the work without causing appreciable deformation due to the force of engagement between the electrode structure and the work, an electric power supply, the electrodes forming said electrode structure being connected to said power supply in such a wayvthat during delivery of welding powerwhile the electrode structure is engaging one electrically conductive side of the ,3. The microwelder describedin claim 2 wherein the electrode structure is freely slidably mounted inside of a sleeve, said sleeve being provided with an upper radially outwardly extending flange, said arm embracing said sleeve, a collar rigidly secured to the electrode structure, said upper flange bearing against said collar whereby until the electrode structure engages the work, the electrode structure is held in a fixed position with respect to said arm with the upper flange of said sleeve bearing against the collar, and when the electrode structure engages the work, continued downward movement of the arm carries the sleeve away from the collar so that the force of engagement between the electrode structure and the work is due solely to the weight of the electrode structure.

4. The microwelder described in claim 2 wherein said arm is in fixed relation to a holding member, a solenoid mounted on said arm for actuating said holding member and causing said arm to hold the electrode structure in a fixed position with respect thereto when the solenoid is energized and for releasably guiding said electrode structure when the solenoid is not energized, whereby when the electrode structure engages the work and energy to the solenoid is removed, the force of engagement between the electrode structure and the work is governed solely by said force regulating means.

5. In a microwelder, a rod-like electrode structure, said electrode structure being at least bilaterally symmetrical and comprising at least two electrodes separated by a relatively thin layer of insulating material and bonded together to form a rigid unitary structure, the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operative end portion for the electrode structure having the appearance of the writing tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil, a cup-like member integrally attached to the upper end of the electrode structure, and said cup-like member being adapted to receive particles of material whereby the weight of the electrode structure can be altered as desired.

6. A microwelder of the class described comprising a support, a rod-like electrode structure, actuating means associated with said support and said electrode structure whereby operation of said actuating means selectively causes said electrode structure to engage or disengage the work; said electrode structure being at least bilaterally symmetrical and comprising at least two electrodes separated by a relatively thin layer of insulating material and bonded together to form a unitary structure, the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operative end portion for the electrode structure having the appearance of the writing tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil; said electrode structure being sufliciently rigid so that the work contacting portions of the electrodes can be formed small enough to precisely localize the application of energy to the work without causing appreciable deformation due to the force of engagement between the electrode structure and the work, an electric power supply, the electrodes forming said electrode structure being connected to said power supply in such a way that during delivery of welding power while the electrode structure is engaging one electrically conductive side of the work, current flows from the power supply down one electrode through the work andlback up the other electrode to complete the circuit, and means associated with said electrode structure for indicating when the electrical contact between the electrode structure and the work is correct.

7. A microwelder of the class described comprising a support, a rod-like electrode structure, actuatingmeans associated with said support and said electrode structure whereby operation of said actuating means. selectively causes said electrode structure to engage or disengage the work; said electrode structure being at least bilaterally symmetrical and comprising at least two electrodes separated by a relatively thin layer of insulating material and bonded together to form a unitary structure, the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operative end portion for the electrode structure having the appearance of the writing tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil; said electrode structure being sufliciently rigid so that the work contacting portions of the electrodes can be formed small enough to precisely localize the energy applied to the work without causing appreciable deformation due to the force of engagement between the electrode structure and the work, an electric power supply, the electrodes forming said electrode structure being connected to said power supply in such a way that during delivery of welding power, while the electrode structure is engaging one electrically conductive side of the work, current flows from the power supply down one electrode through the work and back up the other electrode to complete the circuit; and means connected between said electrode structure, said power supply, and said support for automatically increasing the force of engagement between the electrode structure and the work to compensate for a poor electrical contact between the electrode structure and the 'work until a good electrical contact is obtained and then releasing said electrode structure so-that the force of engagement between the electrode structure and the work depends only on the weight of the electrode structure during each welding operation.

8. A microwelder of the class described comprising a support, a rod-like electrode structure, actuating means associated with said support and said electrode structure whereby operation of said actuating means selectively causes said electrode structure to engage or disengage the work; said electrode structure being at least bilaterally symmetrical and comprising at least two electrodes disposed in spaced apart relationship, and a relatively thin layer of insulating material disposed between adjacent electrodes and respectively bonded thereto to form a unitary structure with said electrodes in a fixed spaced relation with respect to each other, the work contacting portions of said electrodes being flush with the exposed end of said relatively thin layer of insulating material therebetween and defining therewith an operative end portion for the electrode structure having the appearance of the writing tip of a pencil whereby the electrode structure following wear of the work contacting portions of the electrodes can be reshaped like a pencil; said electrode structure being sufficiently rigid so that the work contacting portions of the electrodes can be formed small enough to precisely localize energy applied to the work without causing appreciable deformation due to the force of engagement between the electrode structure and the work, an electric power supply, and the electrodes forming said electrode structure being connected to said power supply in such a way that during delivery of welding power, while the electrode structure is engaging one electrically conductive side of the work, current flows from the power supply dOWn one electrode through the work and back up the other electrode to complete the circuit.

9. In a microwelder, a rod-like electrode structure, said electrode structure being at least bilaterally symmetrical and comprising at least two electrodes, and a relatively thin layer of insulating material separating adjacent electrodes and bonding said electrodes together in a fixed spaced relationship to form a unitary structure, and the work contacting portions of said electrodes and the relatively thin layer of insulating material defining an operative end portion for the electrode structure having the appearance of the writing tip of a pencil whereby the electrode structure following wear of the work coupencil.

References Cited by the Examiner UNITED STATES PATENTS Bean 219234 Caputo 21984 Bardet et al. 219-85 McBerty 21982 Burke 2191 19 Warner 21985v X Ewald 21986 McCalfrey 219119 Lasch et a1 21985 Inoue 219-110 Archer 219-1 10 Hurlebaus 219 86 FOREIGN PATENTS France.

RICHARD M. WOOD, Primary Examiner. 

5. IN A MICROWELDER, A ROD-LIKE ELECTRODE STRUCTURE, SAID ELECTRODE STRUCTURE BEING AT LEAST BILATERALLY SYMMETRICAL AND COMPRISING AT LEAST TWO ELECTRODES SEPARATED BY A RELATIVELY THIN LAYER OF INSULATING MATERIAL AND BONDED TOGETHER TO FORM A RIGID UNITARY STRUCTURE, THE WORK CONTACTING PORTIONS OF SAID ELECTRODES AND THE RELATIVELY THIN LAYER OF INSULATING MATERIAL DEFINING AN OPERATIVE END PORTION FOR THE ELECTRODE STRUCTURE HAVING THE APPEARENCE OF THE WRITING TIP OF A PENCIL WHEREBY THE ELECTRODE STRUCTURE FOLLOWING WEAR OF THE WORK CONTACTING PORTIONS OF THE ELECTRODES CAN BE RESHAPED LIKE A PENCIL, A CUP-LIKE MEMBER INTEGRALLY ATTACHED TO THE UPPER END OF THE ELECTRODE STRUCTURE, AND SAID CUP-LIKE MEMBER BEING ADAPTED TO RECEIVE PARTICLES OF MATERIAL WHEREBY THE WEIGHT OF THE ELECTRODE STRUCTURE CAN BE ALTERED AS DESIRED. 